This invention relates to the art of electroplating a tin-gold alloy deposit. More specifically, it relates to the art of obtaining such a deposit employing an aqueous electroplating bath of improved stability which produces a high quality deposit.
Electroplating baths suitable for depositing a tin-gold alloy have been proposed, for example, in U.S. Pat. No. 3,764,489. The patentee was primarily concerned with preventing the oxidation of stannous ions in the plating bath to stannic ions. According to the patentee, when this oxidation occurs the resulting stannic ions will not codeposit from the plating solution. Thus, the patentee proposes to employ in the electroplating bath a stable stannous compound, a complexing agent which serves to complex with the stannous ions, monovalent gold in the form of the aurocyanide. Further according to the patentee soluble tin anodes are indispensable. The preferred pH range is from about 3.5 to about 5.5.
The deposition of tin-gold alloys has also been proposed in U.S. Pat. No. 1,905,105 by use of an aqueous electroplating solution employing a gold aurocyanide and alkali metal stannates or stannites.
The use of auricyanide compounds in a plating bath at a pH of 1 to 3 has been disclosed in U.S. Pat. No. 3,598,706.